1. Field of the Invention
The present invention relates to a vehicle-mounted antenna structure, and more particularly to an antenna structure having an antenna element printed on window glass of the vehicle.
2. Description of the Related Art
Vehicle antenna structures formed through a method in which an antenna element is printed on a rear window glass of a vehicle have been known and widely employed.
Although, in view of antenna performance, it is most preferable that an antenna element is exposed to the outside of a vehicle on which the antenna is mounted, antenna structures as described above are employed because projecting or whip antennas mounted on the outside of a vehicle body, such as a straight antenna projecting upward from an upper corner of a bumper or a fender of the vehicle and a straight antenna projecting diagonally rearward from a front pillar of the vehicle, can be obstacles to washing of the vehicle and may generate wind noise at certain speeds.
Further, because it is preferable for a straight antenna attached to the bumper or the fender of the vehicle to telescope from an unused contracted position when used and to return when not in use, the antenna must be motorized.
While a straight antenna mounted on the front pillar of the vehicle can be extended or contracted by a driver reaching the antenna from inside, and therefore advantageously eliminates the need for a motor mechanism for extending and returning the antenna at the start and end of use, because the tip of the extended antenna is higher than the roof of the vehicle, their is a danger of the antenna striking a low archway, tunnel, or the like.
In contrast, a glass antenna as described overcomes various problems of such straight antennas, improves directivity of radio waves, and advantageously excels in versatility, such as providing diversity system.
FIG. 1 is a cross sectional view illustrating part of an example vehicle antenna structure formed through a method of manufacturing a laminated glass antenna as described above (see Japanese Patent Laid-Open Publication No. Hei 10-56317). Hereinafter, all such methods for manufacturing laminated glass antennas will be referred to simply as xe2x80x9cglass antenna methodsxe2x80x9d.
Referring to FIG. 1, a packing 3 is sandwiched between a rear edge of a roof panel 1 and a front edge of a rear window glass 2. In this specification, positional expressions, such as front, rear, upper, lower, above, and below, refer to such positions with respect to the vehicle, as understood by a driver or occupant of the vehicle. An additional antenna element, not shown, is disposed on the rear window glass 2 on the cabin side of the vehicle. An antenna unit 4 is disposed inside the cabin.
The antenna unit 4 includes a first contact member 5 disposed on the rear window glass 2 and forming part of the antenna element, a signal processing device 6 packaged in a case fixed to the roof panel 1 on the cabin side, an electrically connecting conductor 7 extending from the signal processing device 6, a supporting member 9 having a contact strip 8 resiliently contacting the first contact member 5, and serving as a second contact member, and other components. The contact strip 8 can be integrally formed by, for example, cutting and shaping the tip of the electrically connecting conductor 7.
The antenna element is connected to an amplifier for processing a received signal through a connection line, which is a conductor electrically undistinguished from the antenna element. As a result, the connection line also substantially functions as an antenna element, whereby transmission and reception cannot be well performed at the originally intended reception frequency band of the antenna element.
While an approach of designing an antenna element that includes a connection line is possible, the distance between the amplifier and the antenna element generally varies according to vehicle model, configuration, and the like, such that the length of the connection line and the positional relationship are widely varied, resulting in considerable variation in reception performance of the antenna, thereby requiring readjustment, setting, and other steps to reduce the variation. Thus, designing an antenna element that includes the connection line is difficult in practice.
Further, even more impractically, the connection lines are not appropriate elements for receiving a signal from outside the cabin because they are mostly in the cabin, and therefore pickup noise within the cabin, adversely affecting the antenna performance.
In view of the above, in the configuration illustrated in FIG. 1, the signal processing device 6 having an amplifier is attached to the roof panel 1 serving as a ceiling of the vehicle, thereby minimizing the distance to the first contact member 5 serving as the antenna element, and using a coaxial cable or a microstrip line for the electrically connecting conductor 7, i.e. the connection line, in order to overcome the above-described problems.
The vehicle antenna structure configured as described above, however, has an additional problem in that the connection configuration is complicated because a coaxial cable or a microstrip line must be used for the electrically connecting conductor 7 (including the supporting member 9) serving as the connection line.
Although the microstrip line is provided for impedance matching, the length required for this function is not necessarily the same as the actual distance between the antenna element and the amplifier. When the lengths differs, the microstrip line and the amplifier must be connected with a coaxial cable, thereby further complicating the connection configuration. In addition, leakage from the microstrip line and its unintended function as an antenna are unavoidable.
In order to solve the above-described problems, the present invention advantageously provides an antenna structure for a vehicle capable of minimizing the distance between a first contact member and a signal processing circuit, and therefore ensuring stable antenna performance without using a connection line of a lengthy wire rod.
To realize this advantage, an antenna structure for a vehicle according to one embodiment of the present invention comprises an antenna element disposed on a window glass of the vehicle, a first contact member disposed at an end of said antenna element, an amplifier case fixed to a body panel of the vehicle, and having at least a portion facing said window glass, and a signal processing circuit disposed in said amplifier case at the portion facing said window glass, and connectable to said first contact member.
In the above configuration, the antenna element is disposed on the window glass of the vehicle, the first contact member is disposed at an end of the antenna element, the amplifier case having at least a portion facing the window glass is fixed to the body panel of the vehicle, and the signal processing circuit is disposed in the amplifier case at the portion facing the window glass.
As a result, it is possible to ensure that the first contact member and the signal processing circuit face each other with minimum distance therebetween, sandwiching the portion of the amplifier case facing the window glass of the vehicle, thereby achieving electrical contact between the first contact member and the signal processing circuit with the minimum distance without using a connection line formed of a wire rod.
In other words, because the distance between the first contact member and the signal processing circuit can be minimized, stable antenna performance can be ensured without using a connection line formed of a lengthy wire rod.
Said first contact member and said signal processing circuit may be electrically connected through a second contact member formed of a conductive piece.
Said second contact member may be resilient.
Said second contact member may be formed as an elastic bellows.
Said second contact member may be made to contact said first contact member by a conductive pressing element.
Said pressing element may be a coil spring.
Said amplifier case may be a shield case for preventing adverse effects of noise on at least said signal processing circuit.
Said second contact member may be covered with a protective member formed of an insulating material.
A conductive rubber may be disposed between said first and second contact members.